1. Field of the Invention
The present invention relates to a method for connecting a digital interface, and more particularly, to a method for connection management among digital devices connected through a digital interface such as IEEE1394.
2. Description of the Related Art
There have been developed various digital devices such as digital TVs, digital VCRs, digital set-top boxes, and so on. Standards such as IEEE1394 for interfacing these digital devices have been introduced. The IEEE1394 standard is disclosed in “IEEE1394-1995: Standard for a High Performance Serial Bus, (IEEE1394 Standard Press, December 1995)”.
In addition, in systems connected to each other via a digital interface such as IEEE1394, connection of isochronous bit streams among digital devices is managed by the IEC61883 specification. The IEC61883 specification is disclosed in “Specification of Digital Interface for Electronic Audio/Video Equipment, (Part 1, December 1995, HD Digital VCR Conference,” and so on.
The IEC61883 specification defines an input plug and an output plug as means for inputting and outputting a bit stream in each digital device. The input plug is controlled by an input master plug register (iMPR) and an input plug control register (iPCR). The output plug is controlled by an output master plug register (oMPR) and an output plug control register (oPCR). The connection of each digital device is managed by controlling the registers related to the input plug and the output plug.
Two types of connection between digital devices include a point-to-point connection and a broadcast connection. In the point-to-point connection, which is formed by an output plug, an input plug, and a channel between these plugs, any digital device can establish/overlay a connection. The device that established the connection takes charge of all the management of the connection and by using this device only, changing, freeing, and particularly restoration of the connection after bus resetting can be performed.
FIG. 1 illustrates a method for establishing a point-to-point connection, wherein a first device 110, a second device 120, and a third device 130 are connected via an IEEE1394 bus. Here, when a point-to-point connection is established between the second device 120 and the third device 130, the first device 110 accesses the iPCR (or the oPCR) of the second device 120 and the iPCR (or the oPCR) of the third device 130. Then, the first device 110 establishes a point-to-point connection (the arrows with dotted line) by writing appropriate values to the registers of the second device 120 and the third device 130, and remains as a connection manager for this connection.
However, when a reset occurs on the IEEE1394 bus after the first device 110 establishes a point-to-point connection between the second device 120 and the third device 130, or when the first device 110 cannot normally operate temporarily or permanently on the bus system, or when the first device 110 is separated from the connection and becomes unable to operate, the point-to-point connection between the second device 120 and the third device 130 cannot be restored. Referring to FIGS. 2A and 2B for example, when the first device 110 is separated from the IEEE1394 bus and a bus reset occurs, the existing point-to-point connection between the second device 120 and the third device 130 cannot be restored permanently, because the connection is originally to be restored by the first device 110 and the first device 110 is currently separated from the bus.
Therefore, when the first device 110 establishes a point-to-point connection between the second device 120 and the third device 130 as shown in FIGS. 1 through 2B, the second device 120 and the third device 130 depend on another device for their connection, and when the first device 110 does not operate normally or operates in an undesired way, it can be impossible to connect the two devices.